The present invention relates to an electrophotographic element and more particularly to an electrophotographic element comprising an electroconductive support member and a photoconductive layer containing a hydrazone compound represented by the following general formula (1) therein, which is formed on the electroconductive support member: ##STR2## wherein Ar represents a substituted or unsubstituted condensed polycyclic group or heterocyclic group, and R represents a methyl group, an ethyl group, a benzyl group or a phenyl group. The condensed polycyclic group includes a naphthalene ring, and an anthracene ring. The heterocyclic ring includes nitrogen, oxygen or sulfur.
Conventionally, inorganic materials, such as selenium, cadmium sulfide, and zinc oxide, are used as the photoconductive materials for use in electrophotography. In the electrophotography, the surface of a photoconductor is charged, for example, by exposing the surface to corona discharge in the dark, and the photoconductor is then exposed to a light image, whereby electric charges are selectively conducted away from the exposed area on the surface of the photoconductor, resulting in that a latent electrostatic image is formed on the surface of the photoconductor. The thus formed latent electrostatic image is developed with toner comprising coloring materials, such as dyes and pigments, and polymeric binder materials. As the indispensible fundamental characteristics of a photoconductor material for use in the electrophotography, the following characteristics are required:
(1) the photoconductor can be charged to an appropriate potential in the dark; (2) electric charges are not conducted away in the dark from the surface of the photoconductor; (3) electric charges are readily conducted away from the surface of the photoconductor under illumination. The above-mentioned inorganic materials have, in fact, an excellent quality, but they still have various shortcomings at the same time.
For instance, selenium, which is now widely used, can meet the above-mentioned requirements of (1) through (3) sufficiently. However, its production is difficult and the production cost is high. More specifically, selenium is not flexible enough for use in a belt-like form and is sensitive to heat and mechanical shocks.
Cadmium sulfide and zinc oxide are respectively dispersed in a binder resin and formed into photoconductors for use in electrophotography. However, the thus prepared photoconductors are respectively poor in the surface smoothness, hardness, tensile strength and abrasion resistance. Therefore, they cannot be used in repetition for a long period of time as they are.
Recently, a variety of electrophotographic photoconductors containing various organic materials have been proposed to eliminate the above-mentioned shortcomings of the inorganic materials. As a matter of fact, some of them are practically used. For instance, the following photoconductors are used in practice: a photoconductor comprising poly-N-vinylcarbazole and 2,4,7-trinitrofluorene-9-on (U.S. Pat. No. 3,484,237); poly-N-vinylcarbazole sensitized by pyrylium salt base pigments (Japanese Patent Publication No. 48-25658); a photoconductor consisting essentially of azo pigments (U.S. Pat. No. 3,775,105); and a photoconductor consisting essentially of an eutectic co-crystalline comprising a dye and a resin (U.S. Pat. No. 3,684,502 and U.S. Pat. No. 3,732,180). These photoconductors have excellent characteristics and high practical value in fact. However, they still have their own shortcomings in view of the requirements for use in electrophotography. Furthermore, U.S. Pat. No. 3,717,462 and U.S. Pat. No. 3,765,884 disclose the use of hydrazone compounds in electrophotographic plates. In U.S. Pat. No. 4,150,987, hydrazone compounds are employed in a charge transfer layer of an electrophotographic element.